A semiconductor employing nitrogen as a group V element in a group III-V semiconductor is referred to as a “group III nitride semiconductor”, and typical examples thereof are aluminum nitride (AlN), gallium nitride (GaN) and indium nitride (InN). The group III nitride semiconductor can be generally expressed as AlxInyGa1-x-yN (0≦x≦1, 0≦y≦1 and 0≦x+y≦1).
A method for fabricating a nitride semiconductor by growing a group III nitride semiconductor on a gallium nitride (GaN) substrate having a major surface defined by a c-plane by metal organic chemical vapor deposition (MOCVD) is known. A group III nitride semiconductor multilayer structure having an n-type layer and a p-type layer as well as an active layer (a light emitting layer) held therebetween can be formed by applying the method, and a light-emitting device utilizing the multilayer structure can be prepared. Such a light-emitting device can be utilized as the light source of a backlight for a liquid crystal panel, for example.
The major surface of the group III nitride semiconductor regrown on the GaN substrate having the major surface defined by a c-plane is also defined by a c-plane. Light extracted from the c-plane is in a random polarization (non-polarization) state. When the light is incident on the liquid crystal panel, therefore, light other than specific polarized light corresponding to a polarizing plate on an incidence side is blocked, and does not contribute to brightness to an outgoing side. Therefore, bright display is disadvantageously hard to implement (efficiency is 50% at the maximum).
In order to solve the problem, a technique of preparing a light-emitting device by growing a group III nitride semiconductor having a major surface defined by a plane other than a c-plane, i.e., a nonpolar plane such as an a-plane or an m-plane or a semipolar plane is examined. When a light-emitting device having a p-type layer and an n-type layer is formed by a group III nitride semiconductor layer having a major surface defined by a nonpolar plane or a semipolar plane, light of a strong polarization state can be emitted. Therefore, loss in the polarizing plate on the incidence side can be reduced by matching the direction of polarization of such a light-emitting device and the direction of passage polarization of the polarizing plate on the incidence side of the liquid crystal panel. Consequently, bright display can be implemented.
Patent Document 1: Japanese Unexamined Patent Publication No. 2007-129042